Tungsten-containing nickel-chromium alloys



industrial scale. 1

It has now been discovered that by means of a novel combination ofalloying elements correlated in a special.

5,165,413 Patented Jan. 19, 1965 TUNGsTnN coNTAnsnsb NICKEL-CHROMIUMALLOYS molybdenum and niobium in a series of alloys all of which alsocontained 6% chromium, 6% aluminum,

Stuart W. K. Shaw, Sutton Coldfield, ind Reginald M.

Cook, Kings Heath, Birmingham, England,.assignors to The InternationalNickel Company, Inc., New York, N.Y., a corporation of Delaware NoDrawing. Filed Feb. 4, 1963, Ser. No. 256,090 Claims priority,application Great Britain Feb. 7, 1962 9 Claims. (Cl. 75171) The presentinvention relates to nickel-base alloys'and more specifically tonickel-base alloys, suitable for use under high stress at temperaturesofat least 1000 C., for example, as stator and rotor blades for gasturbine engines.

Heretofore, the art has endeavored to provide alloys suitable for useunder high stress at temperature i cess of 1000 C. in gas turbinestructures. Such alloys must not only be extremelystrong at temperaturesin excess of 1000 C. but also must be stable at lower temperatures.Although attempts were made to provide satisfactory alloys, none, as faras we are aware, was entirely successful when carried into practicecommercially on an cast alloy for use in precision cast turbinestructures Other objects and advantages will become apparent from thefollowing description. I The alloys according to the invention contain,in percent by weight, about to chromium, about 7% to 16% tungsten, up toabout 5 molybdenum and up to about 4% niobium (the sum of the contentsof tungsten, molybdenum and niobium 1 and two-thirdsof the content ofchromium being from 17.5% to 20.5% ),-about 2% to 8% aluminum, about0.03% 100.3% carbon, up to about 1% zirconium and up to about 0.05%boron,

the balance, apart from impurities, being nickel. The

principal impurities that may be present are iron, siliconand manganeseand the total amount of'these elements should 'be as low aspossibleandmust not exceed 3%. Preferably, the iron content does notexceed 0.5%, the

silicon content 0.3% and the manganese content 0.3 76., r Thestress-rupture lives of the alloys attemper' atures above 1000 C. fallas their chromium content increases. For the longest lives, the chromiumcontent should-..not exceed 9% and ,.advantageously, it is from 5% to7%.

The stress rupture life also depends on the total content of tungsten;molybdenum and niobium and at a given chromium content there is anoptimum value of this total at which the longestlives are obtained. Inalloys con- .taining 6% chromium; the longest lives are obtained whenthe total W+Mo+Nb-content is about With increasing contents, the optimumtotal W+Mo+Nb content decreases and in alloyscontaining 9% chromium, itis 13%. In general, the stress rupture lives of the alloys fall sharplyas the value of the expression. I

is decreased below 17.5% or increased above 20.5%.

. denum and niobium 0,12% carbon and 0.5% zirconium, the balance beingmckel and impurities, is illustrated by the results in Table I. In thistable, all the alloys except Nos. 1, 5, 6, 7 and 12 are in accordancewith the invention.

Table 1 Composition .Stress rupture properties at; 9 t.s.i./1020 0.

Alloy N0. W, Mo, Nb, W+Mo Life to perperper- +Nb rupture Elongation,

cent cent cent +%Or, (HIs.) percent percent;

11 l l 2 2.5- a 19.5 112 1 9 4 2.5 19.5 78 10.5

mannered-7 in life at 7 t.s.i./1020 o. 1

Comparison of the results within the series of Alloys Nos. 1 to 5' and 6to 12 shows how the stress rupture lives increase to a maximum and againdecrease asthe tungsten content is increased at two. diiferent levels ofmolybdenum and niobium. The results for the other alloys show that theirstress rupture properties remain at a high level when the proportions oftungsten, molybare varied within the limits of the.

invention.

The aluminum content of the alloys is important andin alloys of anygiven base composition, variation of the aluminum content has a markedeiIect on the stress rupture life. The longest lives are obtained withaluminum contents in the range 5% ,to 7% and alloys with aluminumcontents Within this range are therefore particu- .larly suitable forgas turbine rotor .blades'which require the best possible stressruptureproperties. At lower aluminum contents, the alloys have highermelting points I and alloys with from 5% down to 3.5% or even"2%Preferably, both molybdenum and niobium are present in, the alloys in,amounts. not exceeding.4% 2.5%," respectively, and the tungsten contentis from 9% to 14%.

The eifect on the stress rupture life in long tons per square inch(t.s.i;) of varying the contents of tungsten,

aluminum are suitable for parts such as gas turbine stator 7 bladeswhich require a high melting point .but are less highly'stressedthanT-rotor blades. i

Variation of. thecarbon content of the alloys within the range 0.03% to0.3% has' little efiect on their stress l rupture properties butpreferably it is from 0.05% to Zirconium and boron improve thestressrupturelives 5 of the alloys, which preferably contain at least0.05

zirconium, with or without boron in such an amount that;

the value of the expression:

%Zr+l0 (%B) is about 0.2%to 0.7%

Surprisingly, it is found that thestress rupture prop-' Icarbon, 0.5%zirconium, balance nickel.

' prope ie balance nickel and impurities.

T able II Stress rupture properties at 9 t.s.i.-/102Q, C.

Ti,peroent '1 Lite, Hrs. Elongation,

' percent Titanium is thus an undesirable impurity and is pre- ,ferab lyabsent. .In commercial manufacture, small quantities of titanium may bepresent in scrap employed as part of the charge and care should be takenthat any titanium introduced intln's way does not exceed 0.5% of the.alloy. and, advantageously, it is less than. 0.25%.

It is an important c-haracteristicfof the alloys that.

theyucontain no vanadium. This element seriously impairs the resistanceof the alloys to'oxidation at 'high temperatures and does not improvetheir stress rupture It is also important that the alloys aresubstantially free from cobalt, and if cobalt is present as an impurityits content should not exceed about 1%. Replacement of p'a'r'tof thenickel in Alloy No.15 in Tab-leI byf1j0% of cobalt was found to'im-pairthe stress rupture, prop erties at 9 t.s.i. and 1020 C., the life torupture being reduced from 187 hours to 119 hours and the elongationfi-orn 17;3% to 12.3%.

An alloy that is particularly suitable for use in the cast form has. thecomposition: 6% chromium, 111%.:- V tungsten, 2% molybdenum, 1.5%niobium,i 6% alumi-- num,' 0.12% carbon, 0.1% zirconium, 0.02% boron,Cast specimens of this composition have been found to exhibit stressrupture lives of over 100 hours under. a stress of 9 t.s.i. at 1020" C.and of 95 hours-under a stress of 7 t.s.i. at 1050 C. Typical impactstrengths of such specimens at 900 C. :are -18 ft. lbs. measured onunnotched 0.45 inch-diameter test 3 pieces. *AfterI heating for 16 hoursat 980. C., the impact strength measured at 900 was increased to 20-27'ft.

The alloys, may be air melted butlare preferably melted under vacuum. 7"Whether. or." not they are vacuunr melted, the. alloys areadvantageously subjected 'to. a vacuum, refining treatment: comprisingholding-them in,

the molten state under, high vacuum .before casting the melt. We preferto hold the. melt. at a temperature of- 140016001 C. at not; more than100 microns pressurefor a period of at least 15Iminutes and,advantageously,

- for 60 minutes or more. The. duration of the treatment depends tosome. extent on the purityof the ingredients of the melt, being longerwhen less. pure ingredients are;

employed.

When making'small; castings, for example, turbine I blades or stressrupture test pieces, the alloys are preferabliy cast under. vacuum butwhen making large castingsfrom a melt that has been produced or refinedunder vacuum, itmakes little difference tolthe properties obtainedwhether casting is carried out in vacuum, inert gas or a-i r. All thestress rupture test results given in I this spec-ificat'ion-wereobtained on test pieces machined from cast specimens that had beenvacuum cast from vacuum melted material thathad been vacuum refined forat least 15 minutes at 1500C. under a pressure of less than .1 micron.

Articles andparts cast from the alloys may be used in 'the as-rcastcondition for temperature service, for s example, as rotor blades ingasturbine engines. If desired, the alloys may be homogenized by heatingthe temperature range 850 to 1250" C. before being put into service. Thealloysalso exhibit useful stress rupture properties in the wrought formafter solution heating and aging.

For use at temperatures. above 1000 C.'under conditions such as areencountered. in gas turbine engines, involving both oxidation and sulfurattack, articles and parts made from the alloys are preferably providedwith a protective coating, for example, of aluminum.

Although the presentinvention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted ito without departing 'from the spirit andscope of the invention, as those skilled in the art will readilyunderstand. Such modifications and variations are considered to beWithin the purviewand scope of the invention and appended claims. 7

We claim: V

e l. A cast alloy consisting essentially of about 5% to .30% chromium,about 7% to 16% tungsten, up-to about i 5% molybdenum,up to about 4%niobium with the sum of the percentages of tungsten, molybdenum and Iniobium plus" two-thirds the percentage of chromium mbeing about l7.5%to 20.5%, about 2% to 8% alum-i- 25 num, ab'ou t 0.03% to 0.3% carbon,up to about 1% zirconium, and up to about 0.05 boron with the balancebeing essentially nickel. v

e I 2. An' alloy as in clainrl wherein the total of the percentages oftungsten, molybdenum .and niobium is about. 15% V s An alloy as in claim1 wherein thechromium content is about 5% to about 9%} and two-thirdsthe percentage offchromium being about 17.5% to 20.5%, about 2%. to 8%aluminum, about 0.03% to 0.3% carbon, upto 1% zirconium, up to 0.05%boron, up to not more than 0.5% titanium, up to not more"than1% cobalt,and the balance essentially nickel. 6. An alloy as set forth in'claim 5wherein the chromium content is about 5% to about 9% 7 An alloy as setforth in claim 6 wherein the tungsten content is about 9% to about 14%,r

1 '8. An alloy. 'as set forth in claim"7 wher'ein themolybdenu-rncontent does not exceed 4% and'theniobium content does' notexceed about 2.5% Q a 9; An alloy as set forth in claim 8 wherein thechromium content is from 5% to about 7%.;

6O lieferences Cited in the file of this patent v, UNITED sTAfrEseATENTs 2,575,915 Guy Nov. 20, 1951 2,920,956 Nisbetet al.; Jan. 12,1960 2,948,606 Thielemann L Aug. 9, 1960 i I FOREIGN PA N S 1 853,103Great Britain Nov. 2, 1960 OTHERREFERENCES Guy: Nickel-Base.AlloysforHigh Temperature Apphcationsjf Preprlntiof. paper'presented at the 30thAnnual Convention of the .American Society for Metals,

1. A CAST ALLOY CONSISTING ESSENTIALLY OF ABOUT 5% TO 10% CHROMIUM,ABOUT 7% TO 16% TUNGSTEN, UP TO ABOUT 5% MOLYBDENUM, UP TO ABOUT 4%NIOBIUM WITH THE SUM OF THE PERCENTAGES OF TUNGSTEN, MOLYBDENUM ANDNIOBIUM PLUS TWO-THIRDS THE PERCENTAGE OF CHROMIUM BEING ABOUT 17.5% TO20.5%, ABOUT 2% TO 8% ALUMINUM, ABOUT 0.03% TO 0.3% CARBON, UP TO ABOUT1% ZIRCONIUM, AND UP TO ABOUT 0.05% BERON WITH THE BLANACE BEINGESSENTIALLY NICKEL.